This invention relates to disc saw heads for tree felling.
In U.S. Pat. No. 5,697,412, incorporated by reference herein, the present inventor explained the desirability of being able to store maximum severance size trees, i.e. trees of the maximum size severable by the severance means, in a position totally clear of the severance area at the front of the tree-cutting head. (Throughout this specification, "severance area" refers generally to the area of the saw occupied by a tree as it is being severed, up to the point of severance.) In the '412 patent, trees were stored in an accumulation area to one side and to the rear of the centerline of a shear or other severance means, and were swept from the severance area to the accumulation area by taker and tucker arms which both pivoted from the opposite side of the centerline.
In the patent, it was contemplated that severance means other than a shear, such as a saw, could be used. However, in adapting the invention for use with a saw, it was realized that further innovations were desirable in order to make optimum use of some of the principles of the invention.
Examining the geometry and relative dimensions of a disc saw and its maximum tree diameter cutting capacity reveals some inescapable design restrictions. If the maximum tree diameter tree which can be cut (without resorting to multiple cuts) is 22 inches, for example, and if the motor or saw hub has a diameter of say 14 inches, for example, then the diameter of the saw disc has to be at least 58 inches, i.e. 22 inches plus 14 inches plus 22 inches. Add to this a protective housing with some clearance for wood chip escape, and a head more than 5 feet wide at its base would have to be carried around. This is wider than desirable, taking into account various factors including frequently limited space between adjacent trees.
Thus when designing a disc saw head where a large tree accumulation capacity is desired, it is not sufficient to simply increase the diameter of the disc beyond what is dimensionally needed to sever the tree, since this produces an excessively large head. Instead, it is preferable to make the saw just big enough to get through the largest desired tree, and then try to use whatever storage space can be found. Typically in the prior art, this has meant using the severance space itself, and any additional space on the surface of the disc.
However, the amount of additional space that others have had available to them, prior to present invention, had been hindered by the essential construction and operating manner of such disc saws. In U.S. Pat. Nos. 5,377,731 (Wildey) and U.S. Pat. No. 5,303,752 (MacLennan), it is apparently assumed that severed trees should only be supported on a butt plate (which covers the inner saw disc), and not on the rim which consists of the sides of the cutting teeth. This is so that neither tossing nor burning contact between the tree butt and the disc and tooth top surfaces occurs. MacLennan makes some extraordinary effort to make a slightly larger radius butt plate than some others have, so that more trees will fit onto it. Both patents show the top edge of the teeth only barely high enough to cut a path for the butt plate.
Conventional butt plates are sunk into the top of disc saws, and thus are confined to radii always less than the saw radius, by the radial dimension of the teeth and their rim. Thus in the above example if 3 inches was used for the rim and teeth, then a maximum stored tree diameter which is 3 inches less than the maximum size, i.e. only 19 inches instead of 22 inches would have to be accepted. This would not meet the inventor's desire to store a maximum-size tree separate from the severance space.
A primitive partial solution to permitting a single maximum diameter tree to be carried was introduced by Koehring-Waterous a number of years ago. In their saw, illustrated in plan view in FIG. 17 (prior art), a small ramp plate 101 was positioned at the front of the saw directly beside the severance area, angled upwardly over the rim and teeth 102 of the saw. This allowed a single maximum-diameter tree 103 to be pushed by a taker arm 104 and held by a tucker arm 105 so that one side would encroach slightly into the area above the saw rim and teeth, so that it could be lifted slightly to as to be carried without contacting the saw. However, the plate merely lifted one edge of the tree over the rim, with most of the tree still being positioned essentially on or above the butt plate, and in the severance area, with no separate accumulation or storage area. As can be seen clearly from the overlapping dotted-line circles 103 and 103' in FIG. 17, it thus was not possible to cut and store a maximum-diameter tree and continue cutting another maximum-size tree, if any other tree. There was no separate storage space removed from the severance area.
Another problem in the prior art is that conventional butt plates, because of the height of their upper surfaces relative to the saw kerf, do not permit the saw disc to be angled slightly forwardly to facilitate continuous cutting, without the butt plate wedging down onto the saw disc, which is clearly undesirable for obvious reasons. This will be explained in greater detail below.